United States
Environmental Protection
Agency
Chesapeake Bay
Program
Annapolis MD 21403
Research and Development
EPA-600/S3-82-089 Jan. 1983
Project Summary
Fate, Transport, and
Transformation of Toxics:
Significance of Suspended
Sediment and Fluid Mud
Maynard Nichols, Richard Harris, Galen Thompson, and Bruce Nelson
This research sought to determine
the distribution of selected metals in
suspended material and fluid mud, to
identify potential zones of toxic
accumulation, and to trace their
transport routes.
Between March 1979 and April
1980, observations of flow, salinity,
suspended material, pH, and dissolved
oxygen were made in Bay-wide longi-
tudinal sections, and at four anchor
stations in the Northern Bay. The
observations covered a range of
conditions, including seasonal high
and low river discharges, sediment
influx, neap-spring tide range, and
oxygenated-anoxic water. Samples of
suspended material, fluid mud, and
bed sediment were analyzed for
particle size, organic matter, and
metal content.
Metal concentrations of As, Cu, Mn,
Ni, Pb. Sn, and Zn in fluid mud and bed
sediment, per gram of material,
decrease seaward from a maximum in
the Baltimore-Susquehanna River
area. The concentrations of metals
Mn, Pb, and Zn are four to six times
greater than Fe-corrected average
shale, indicating major human input,
and significant accumulation in this
zone.
Metal concentrations of Cd, Cu, Pb,
Ni, and Zn are maximal in
surfacesuspended material from the
central Bay. They are higher than
landward near-potential sources, and
they exceed concentrations in bed
sediment two to 80 times. The
enrichment is not natural compared to
average shale or plankton; it is most
likely created by bio-accumulation.
Transport of particle-associated
metals from major sources follows
either hydrodynamic pathways
leading to particle accumulation by
the estuarine circulation or
bioecological routes leading to
bio-accumulation.
Management and monitoring
strategies are provided to reduce
potentially toxic metals to acceptable
levels and warn management
agencies of toxic hazards.
This report is submitted in fulfill-
ment of Grant R806002-01 -1 by the
Virginia Institute of Marine Science,
School of Marine Science, College of
William and Mary, under sponsorship
of the U.S. Environmental Protection
Agency. This report covers the period
July 1, 1978 - August 30, 1982.
This Project Summary was develop-
ed by EPA's Chesapeake Bay Program.
Annapolis, MD. to announce key find-
ings of the research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
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Introduction
Each year, a substantial load of trace
metals enters Chesapeake Bay, from
both natural and human sources.
Regional production of toxic metals is
increasing with increasing industrial
activity and sewage discharge. At least
half of all cadmium (Cd), lead (Pb),
copper (Cu), and chromium (Cr)
reaching the Bay results from sewage
and industrial waste. Although low
concentrations of metals are important
to environmental quality of the Bay,
there is cause for concern if concentra-
tions are excessive. Toxic effects have
not been demonstrated, but disturbing
changes in the Bay environment have
been observed: a decrease in oyster and
striped bass populations, a lack of shad
runs in the upper bay, and declining
clam catches. Knowledge of contamina-
tion levels, transport routes, and
reservoirs of potential contaminants is
necessary because toxicants may alter
the quality of the Bay over periods of
time.
This study investigates the role of
suspended sediment and fluid mud in
the fate of toxic metals in the
Chesapeake Bay system. Fluid mud, an
intermediate stage between mobile
suspended material and mud, is
chemically important because it is a
reservoir for potentially toxic metals and
a medium for chemical transfer.
Procedure/Methodology
A series of field observations defined
the Bay-wide distribution of metal
contaminants in the following way:
suspended material was collected for
analysis of toxic metals; water in which
the metals occur was characterized; and
sediments with which metals associate
were analyzed for particle size and
physical properties. Temporal variations
of sediment and metal loading were
established, and potential zones of
metal accumulation and their transport
routes were identified. Field
observations included contrasting
conditions such as seasonal high-low
river discharges and sediment influx,
neap-spring tide range, and oxygenated-
anoxic water differences. A survey of
122 stations, identifying these variables,
and recording the parameters of tem-
perature, salinity, dissolved oxygen, pH,
and total amounts of suspended mate-
rial, resulted in 5576 measurements,
including analyses of six to 11 metals.
Bed sediment and fluid mud were
obtained with a stainless steel
Smith-Maclntyre* grab or Bouma box
core. Suspended materials collected on
Nuclepore filters were analyzed by
flame atomic absorption for iron (Fe),
manganese (Mn), and zinc (Zn).
Flameless atomic absorption was used
to obtain concentrations of arsenic (As),
cadmium (Cd), copper (Cu), mercury
(Hg), nickel (Ni), lead (Pb), and tin (Sn).
Results and Conclusions
The maximum turbidity zone (stations
12 to 18) contains high suspended
loads, fine particle size, and low organic
carbon percentages. Low suspended
loads, coarse particle size, and high
organic percentages are common to the
central Bay zone (stations eight to 11);
stations one to seven, representing the
near-entrance reaches, have
intermediate suspended loads,
moderate particle size, and moderate
organic percentages. Conditions in the
deeper portions of the central Bay
region favor accumulation of metals and
fluid mud because of fine-grained,
moderately organic sediments which
deposit rapidly.
Metal distributions in suspended
material are vertically stratified, with
mean-surface and mid-depth concen-
trations greater than near-bottom
depths. Cd, Cu, and Pb of surface and
mid-depth waters are three to 12 times
higher in summer than in spring. Con-
centrations of Cd, Cu, Pb, Ni, and Zn are
maximal in surface suspended matter
from the central Bay, suggesting bio-
accumulation of metals from distant
sources.
Bay water is well-buffered against pH
change and is oxygenated, except in
summer when near-bottom water of the
central Bay (below 10m depth) is anoxic.
Also, time, depth, and distance seaward
are conditions which affect physical,
chemical, and sedimentologic rates of
transport and accumulation of toxics.
Recommendations
By dealing with Chesapeake Bay as
an entity, the state of the Bay can be
improved by reducing input of such
potentially toxic metals as Cd, Cu, Ni, Pb,
and Zn from wastewater and industrial
discharges. Nutrients which stimulate
organic production should be reduced to
alleviate the suspended solids load, of
which some 40 to 60 percent is
composed of organic material.
Entrapment of river-borne sediment can
be deterred by regulating inflows during
periods of high sediment influx.
Potentially toxic metals should be
managed by controlling them at their
sources, by learning the long-term
changes and "far-field" effects in zones
of accumulation, by recognizing
amounts of toxicants in the system
which are above natural levels, as well
as the associations between metals and
sediment. A monitoring system of the
Bay and its tributaries, with a scientific
data base, should be established to
warn Bay managers of toxic hazards.
Research should consider such factors
as bio-accumulation of toxics in
plankton, the significance of repetitive
sediment resuspensions, and the role of
tributaries as sinks or sources of metals
and sediments.
*Mention of tradenames or commercial products
does not constitute endorsement or
recommendation for use by the U S Environmental
Protection Agency.
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Maynard Nichols, Richard Harris, Galen Thompson, and Bruce Nelson are with
the Virginia Institute of Marine Science, Gloucester Point, VA 23062.
Duane Wilding was the EPA Project Officer (see below for present contact).
The complete report, entitled "Fate, Transport, and Transformation of Toxics:
Significance of Suspended Sediment and Fluid Mud," (Order No. PB 83-116
426; Cost: $13.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
For information contact David Flemer at:
Chesapeake Bay Program
2083 West Street, Suite 5G
Annapolis, MD21403
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